The time factor is divided into many fractions of moments, hours, months, years, periods, seasons, etc. All the divisions in this verse are determined according to the astronomical calculations of Vedic literature. There are six seasons, called rutus, and there is the period of four months called caturmasya. Three periods of four months complete one year. According to Vedic astronomical calculations, there are thirteen months. The thirteenth month is called adhi-masa or mala-masa and is added every third year. Time is compared here to a big wheel which has 360 joints, six rims in the shape of seasons, and numberless leaves in the shape of moments. It rotates on the eternal existence, Brahman.
Ref >> Srila Prabhupada Vani